Design and optimization of lightweight bending strain energy harvesters using irradiation cross-linked polypropylene ferroelectret

Abstract

In this work, a concept for bending strain energy harvesting with lightweight ferroelectrets subject to metallic host structures is proposed. The energy harvester (EH) works with the ferroelectret irradiation cross-linked polypropylene (IXPP) and uses the piezoelectric δ 33-mode by transferring in-plane bending strain energy of a host structure to a compression of an IXPP stack. This is achieved with a simple and lightweight transmission made of structural steel. In this way, a high ratio of generated power per used EH mass can be achieved, being the main design goal of this paper. To demonstrate this, miniature EHs as unit cells for larger EH systems are investigated. The strain magnitude of the excitation in an aircraft wing of at 1.5 Hz from previous work is partly taken into account for calculations. In an analytical modeling approach, the energy conversion abilities of the presented concept is compared to concepts using lead zirconate titanate ceramics to stress the usefulness in cases where strain energy is the prominent source of vibration energy. Further, an optimization algorithm is presented for a static and a dynamic case without a host structure and for a dynamic case with an aluminum host structure. The optimized power output and power output per total EH mass for the three cases is calculated to and , 0.7 mW and 80 mW kg−1 as well as (at 1 N excitation magnitude) and (at 1 N excitation magnitude) respectively. Finally, experimental results for case three are presented to validate the model of the proposed and optimized EH topology up to 500 Hz. The results further show a good mechanical reproducibility of the measured transfer behavior and a fairly good reproducibility of the mechanical-electrical results due to deviations in material properties. A comparison of the model with the experimental results shows a good agreement. Therefore a linear ferroelectret model appears to be suitable to predict the system behavior in lower and higher frequency ranges as well as for high ferroelectret material strains. The optimized EH provides a comparably high ratio of power output per mass when added to a structure like an aircraft which is shown in a comparison to other research works. The performance in a real application can be further improved to 52 mW within a 1 m2 area using a clustering approach, discussed in the paper. Large deformations of lightweight structures like aircraft wings at low and high frequencies can thus be exploited to provide enough electrical power decentrally for low-power consumers.